diff --git a/composer.json b/composer.json
index 6c65474..b350a9a 100644
--- a/composer.json
+++ b/composer.json
@@ -27,7 +27,8 @@
     },
     "require": {
         "php": ">=7.4",
-        "guzzlehttp/psr7": "^2 || ^1.7"
+        "guzzlehttp/psr7": "^2 || ^1.7",
+        "symfony/polyfill-php80": "^1.15"
     },
     "require-dev": {
         "phpunit/phpunit": "^9.5",
diff --git a/src/Handshake/ClientNegotiator.php b/src/Handshake/ClientNegotiator.php
index c32a1cf..a7a9125 100644
--- a/src/Handshake/ClientNegotiator.php
+++ b/src/Handshake/ClientNegotiator.php
@@ -6,17 +6,11 @@ use Psr\Http\Message\UriInterface;
 use GuzzleHttp\Psr7\Request;
 
 class ClientNegotiator {
-    /**
-     * @var ResponseVerifier
-     */
-    private $verifier;
+    private ResponseVerifier $verifier;
 
-    /**
-     * @var \Psr\Http\Message\RequestInterface
-     */
-    private $defaultHeader;
+    private RequestInterface $defaultHeader;
 
-    function __construct(PermessageDeflateOptions $perMessageDeflateOptions = null) {
+    public function __construct(PermessageDeflateOptions $perMessageDeflateOptions = null) {
         $this->verifier = new ResponseVerifier;
 
         $this->defaultHeader = new Request('GET', '', [
@@ -26,15 +20,12 @@ class ClientNegotiator {
           , 'User-Agent'            => "Ratchet"
         ]);
 
-        if ($perMessageDeflateOptions === null) {
-            $perMessageDeflateOptions = PermessageDeflateOptions::createDisabled();
-        }
+        $perMessageDeflateOptions ??= PermessageDeflateOptions::createDisabled();
 
         // https://bugs.php.net/bug.php?id=73373
         // https://bugs.php.net/bug.php?id=74240 - need >=7.1.4 or >=7.0.18
-        if ($perMessageDeflateOptions->isEnabled() &&
-            !PermessageDeflateOptions::permessageDeflateSupported()) {
-            trigger_error('permessage-deflate is being disabled because it is not support by your PHP version.', E_USER_NOTICE);
+        if ($perMessageDeflateOptions->isEnabled() && !PermessageDeflateOptions::permessageDeflateSupported()) {
+            trigger_error('permessage-deflate is being disabled because it is not supported by your PHP version.', E_USER_NOTICE);
             $perMessageDeflateOptions = PermessageDeflateOptions::createDisabled();
         }
         if ($perMessageDeflateOptions->isEnabled() && !function_exists('deflate_add')) {
@@ -45,16 +36,16 @@ class ClientNegotiator {
         $this->defaultHeader = $perMessageDeflateOptions->addHeaderToRequest($this->defaultHeader);
     }
 
-    public function generateRequest(UriInterface $uri) {
+    public function generateRequest(UriInterface $uri): RequestInterface {
         return $this->defaultHeader->withUri($uri)
             ->withHeader("Sec-WebSocket-Key", $this->generateKey());
     }
 
-    public function validateResponse(RequestInterface $request, ResponseInterface $response) {
+    public function validateResponse(RequestInterface $request, ResponseInterface $response): bool {
         return $this->verifier->verifyAll($request, $response);
     }
 
-    public function generateKey() {
+    public function generateKey(): string {
         $chars     = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwzyz1234567890+/=';
         $charRange = strlen($chars) - 1;
         $key       = '';
@@ -65,7 +56,7 @@ class ClientNegotiator {
         return base64_encode($key);
     }
 
-    public function getVersion() {
+    public function getVersion(): int {
         return 13;
     }
 }
diff --git a/src/Handshake/NegotiatorInterface.php b/src/Handshake/NegotiatorInterface.php
index c152eca..8903a4a 100644
--- a/src/Handshake/NegotiatorInterface.php
+++ b/src/Handshake/NegotiatorInterface.php
@@ -1,6 +1,7 @@
 <?php
 namespace Ratchet\RFC6455\Handshake;
 use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * A standard interface for interacting with the various version of the WebSocket protocol
@@ -14,34 +15,34 @@ interface NegotiatorInterface {
      * @param RequestInterface $request
      * @return bool
      */
-    function isProtocol(RequestInterface $request);
+    public function isProtocol(RequestInterface $request): bool;
 
     /**
      * Although the version has a name associated with it the integer returned is the proper identification
      * @return int
      */
-    function getVersionNumber();
+    public function getVersionNumber(): int;
 
     /**
      * Perform the handshake and return the response headers
      * @param RequestInterface $request
-     * @return \Psr\Http\Message\ResponseInterface
+     * @return ResponseInterface
      */
-    function handshake(RequestInterface $request);
+    public function handshake(RequestInterface $request): ResponseInterface;
 
     /**
      * Add supported protocols. If the request has any matching the response will include one
      * @param array $protocols
      */
-    function setSupportedSubProtocols(array $protocols);
+    public function setSupportedSubProtocols(array $protocols): void;
 
     /**
      * If enabled and support for a subprotocol has been added handshake
      *  will not upgrade if a match between request and supported subprotocols
      * @param boolean $enable
      * @todo Consider extending this interface and moving this there.
-     *       The spec does says the server can fail for this reason, but
+     *       The spec does say the server can fail for this reason, but
      *       it is not a requirement. This is an implementation detail.
      */
-    function setStrictSubProtocolCheck($enable);
+    public function setStrictSubProtocolCheck(bool $enable): void;
 }
diff --git a/src/Handshake/PermessageDeflateOptions.php b/src/Handshake/PermessageDeflateOptions.php
index 051d428..e816918 100644
--- a/src/Handshake/PermessageDeflateOptions.php
+++ b/src/Handshake/PermessageDeflateOptions.php
@@ -8,21 +8,21 @@ use Psr\Http\Message\ResponseInterface;
 
 final class PermessageDeflateOptions
 {
-    const MAX_WINDOW_BITS = 15;
-    /* this is a private instead of const for 5.4 compatibility */
-    private static $VALID_BITS = ['8', '9', '10', '11', '12', '13', '14', '15'];
+    public const MAX_WINDOW_BITS = 15;
 
-    private $deflateEnabled = false;
+    private const VALID_BITS = [8, 9, 10, 11, 12, 13, 14, 15];
 
-    private $server_no_context_takeover;
-    private $client_no_context_takeover;
-    private $server_max_window_bits;
-    private $client_max_window_bits;
+    private bool $deflateEnabled = false;
+
+    private ?bool $server_no_context_takeover = null;
+    private ?bool $client_no_context_takeover = null;
+    private ?int $server_max_window_bits = null;
+    private ?int $client_max_window_bits = null;
 
     private function __construct() { }
 
     public static function createEnabled() {
-        $new                             = new static();
+        $new                             = new self();
         $new->deflateEnabled             = true;
         $new->client_max_window_bits     = self::MAX_WINDOW_BITS;
         $new->client_no_context_takeover = false;
@@ -33,35 +33,35 @@ final class PermessageDeflateOptions
     }
 
     public static function createDisabled() {
-        return new static();
+        return new self();
     }
 
-    public function withClientNoContextTakeover() {
+    public function withClientNoContextTakeover(): self {
         $new = clone $this;
         $new->client_no_context_takeover = true;
         return $new;
     }
 
-    public function withoutClientNoContextTakeover() {
+    public function withoutClientNoContextTakeover(): self {
         $new = clone $this;
         $new->client_no_context_takeover = false;
         return $new;
     }
 
-    public function withServerNoContextTakeover() {
+    public function withServerNoContextTakeover(): self {
         $new = clone $this;
         $new->server_no_context_takeover = true;
         return $new;
     }
 
-    public function withoutServerNoContextTakeover() {
+    public function withoutServerNoContextTakeover(): self {
         $new = clone $this;
         $new->server_no_context_takeover = false;
         return $new;
     }
 
-    public function withServerMaxWindowBits($bits = self::MAX_WINDOW_BITS) {
-        if (!in_array($bits, self::$VALID_BITS)) {
+    public function withServerMaxWindowBits(int $bits = self::MAX_WINDOW_BITS): self {
+        if (!in_array($bits, self::VALID_BITS)) {
             throw new \Exception('server_max_window_bits must have a value between 8 and 15.');
         }
         $new = clone $this;
@@ -69,8 +69,8 @@ final class PermessageDeflateOptions
         return $new;
     }
 
-    public function withClientMaxWindowBits($bits = self::MAX_WINDOW_BITS) {
-        if (!in_array($bits, self::$VALID_BITS)) {
+    public function withClientMaxWindowBits(int $bits = self::MAX_WINDOW_BITS): self {
+        if (!in_array($bits, self::VALID_BITS)) {
             throw new \Exception('client_max_window_bits must have a value between 8 and 15.');
         }
         $new = clone $this;
@@ -86,7 +86,7 @@ final class PermessageDeflateOptions
      * @return PermessageDeflateOptions[]
      * @throws \Exception
      */
-    public static function fromRequestOrResponse(MessageInterface $requestOrResponse) {
+    public static function fromRequestOrResponse(MessageInterface $requestOrResponse): array {
         $optionSets = [];
 
         $extHeader = preg_replace('/\s+/', '', join(', ', $requestOrResponse->getHeader('Sec-Websocket-Extensions')));
@@ -103,7 +103,7 @@ final class PermessageDeflateOptions
             }
 
             array_shift($parts);
-            $options                 = new static();
+            $options                 = new self();
             $options->deflateEnabled = true;
             foreach ($parts as $part) {
                 $kv = explode('=', $part);
@@ -119,15 +119,18 @@ final class PermessageDeflateOptions
                         $value = true;
                         break;
                     case "server_max_window_bits":
-                        if (!in_array($value, self::$VALID_BITS)) {
+                        $value = (int) $value;
+                        if (!in_array($value, self::VALID_BITS)) {
                             throw new InvalidPermessageDeflateOptionsException($key . ' must have a value between 8 and 15.');
                         }
                         break;
                     case "client_max_window_bits":
                         if ($value === null) {
-                            $value = '15';
+                            $value = 15;
+                        } else {
+                            $value = (int) $value;
                         }
-                        if (!in_array($value, self::$VALID_BITS)) {
+                        if (!in_array($value, self::VALID_BITS)) {
                             throw new InvalidPermessageDeflateOptionsException($key . ' must have no value or a value between 8 and 15.');
                         }
                         break;
@@ -154,39 +157,39 @@ final class PermessageDeflateOptions
         }
 
         // always put a disabled on the end
-        $optionSets[] = new static();
+        $optionSets[] = new self();
 
         return $optionSets;
     }
 
     /**
-     * @return mixed
+     * @return bool|null
      */
-    public function getServerNoContextTakeover()
+    public function getServerNoContextTakeover(): ?bool
     {
         return $this->server_no_context_takeover;
     }
 
     /**
-     * @return mixed
+     * @return bool|null
      */
-    public function getClientNoContextTakeover()
+    public function getClientNoContextTakeover(): ?bool
     {
         return $this->client_no_context_takeover;
     }
 
     /**
-     * @return mixed
+     * @return int|null
      */
-    public function getServerMaxWindowBits()
+    public function getServerMaxWindowBits(): ?int
     {
         return $this->server_max_window_bits;
     }
 
     /**
-     * @return mixed
+     * @return int|null
      */
-    public function getClientMaxWindowBits()
+    public function getClientMaxWindowBits(): ?int
     {
         return $this->client_max_window_bits;
     }
@@ -194,7 +197,7 @@ final class PermessageDeflateOptions
     /**
      * @return bool
      */
-    public function isEnabled()
+    public function isEnabled(): bool
     {
         return $this->deflateEnabled;
     }
@@ -203,7 +206,7 @@ final class PermessageDeflateOptions
      * @param ResponseInterface $response
      * @return ResponseInterface
      */
-    public function addHeaderToResponse(ResponseInterface $response)
+    public function addHeaderToResponse(ResponseInterface $response): ResponseInterface
     {
         if (!$this->deflateEnabled) {
             return $response;
@@ -226,7 +229,7 @@ final class PermessageDeflateOptions
         return $response->withAddedHeader('Sec-Websocket-Extensions', $header);
     }
 
-    public function addHeaderToRequest(RequestInterface $request) {
+    public function addHeaderToRequest(RequestInterface $request): RequestInterface {
         if (!$this->deflateEnabled) {
             return $request;
         }
@@ -249,7 +252,7 @@ final class PermessageDeflateOptions
         return $request->withAddedHeader('Sec-Websocket-Extensions', $header);
     }
 
-    public static function permessageDeflateSupported($version = PHP_VERSION) {
+    public static function permessageDeflateSupported(string $version = PHP_VERSION): bool {
         if (!function_exists('deflate_init')) {
             return false;
         }
diff --git a/src/Handshake/RequestVerifier.php b/src/Handshake/RequestVerifier.php
index 9e192c5..c2f26a1 100644
--- a/src/Handshake/RequestVerifier.php
+++ b/src/Handshake/RequestVerifier.php
@@ -8,14 +8,14 @@ use Psr\Http\Message\RequestInterface;
  * @todo Currently just returning invalid - should consider returning appropriate HTTP status code error #s
  */
 class RequestVerifier {
-    const VERSION = 13;
+    public const VERSION = 13;
 
     /**
      * Given an array of the headers this method will run through all verification methods
      * @param RequestInterface $request
      * @return bool TRUE if all headers are valid, FALSE if 1 or more were invalid
      */
-    public function verifyAll(RequestInterface $request) {
+    public function verifyAll(RequestInterface $request): bool {
         $passes = 0;
 
         $passes += (int)$this->verifyMethod($request->getMethod());
@@ -27,7 +27,7 @@ class RequestVerifier {
         $passes += (int)$this->verifyKey($request->getHeader('Sec-WebSocket-Key'));
         $passes += (int)$this->verifyVersion($request->getHeader('Sec-WebSocket-Version'));
 
-        return (8 === $passes);
+        return 8 === $passes;
     }
 
     /**
@@ -35,8 +35,8 @@ class RequestVerifier {
      * @param string
      * @return bool
      */
-    public function verifyMethod($val) {
-        return ('get' === strtolower($val));
+    public function verifyMethod(string $val): bool {
+        return 'get' === strtolower($val);
     }
 
     /**
@@ -44,15 +44,15 @@ class RequestVerifier {
      * @param string|int
      * @return bool
      */
-    public function verifyHTTPVersion($val) {
-        return (1.1 <= (double)$val);
+    public function verifyHTTPVersion($val): bool {
+        return 1.1 <= (double)$val;
     }
 
     /**
      * @param string
      * @return bool
      */
-    public function verifyRequestURI($val) {
+    public function verifyRequestURI(string $val): bool {
         if ($val[0] !== '/') {
             return false;
         }
@@ -73,8 +73,8 @@ class RequestVerifier {
      * @return bool
      * @todo Once I fix HTTP::getHeaders just verify this isn't NULL or empty...or maybe need to verify it's a valid domain??? Or should it equal $_SERVER['HOST'] ?
      */
-    public function verifyHost(array $hostHeader) {
-        return (1 === count($hostHeader));
+    public function verifyHost(array $hostHeader): bool {
+        return 1 === count($hostHeader);
     }
 
     /**
@@ -82,8 +82,8 @@ class RequestVerifier {
      * @param  array $upgradeHeader MUST equal "websocket"
      * @return bool
      */
-    public function verifyUpgradeRequest(array $upgradeHeader) {
-        return (1 === count($upgradeHeader) && 'websocket' === strtolower($upgradeHeader[0]));
+    public function verifyUpgradeRequest(array $upgradeHeader): bool {
+        return 1 === count($upgradeHeader) && 'websocket' === strtolower($upgradeHeader[0]);
     }
 
     /**
@@ -91,13 +91,11 @@ class RequestVerifier {
      * @param  array $connectionHeader MUST include "Upgrade"
      * @return bool
      */
-    public function verifyConnection(array $connectionHeader) {
+    public function verifyConnection(array $connectionHeader): bool {
         foreach ($connectionHeader as $l) {
             $upgrades = array_filter(
                 array_map('trim', array_map('strtolower', explode(',', $l))),
-                function ($x) {
-                    return 'upgrade' === $x;
-                }
+                static fn (string $x) => 'upgrade' === $x
             );
             if (count($upgrades) > 0) {
                 return true;
@@ -113,8 +111,8 @@ class RequestVerifier {
      * @todo The spec says we don't need to base64_decode - can I just check if the length is 24 and not decode?
      * @todo Check the spec to see what the encoding of the key could be
      */
-    public function verifyKey(array $keyHeader) {
-        return (1 === count($keyHeader) && 16 === strlen(base64_decode($keyHeader[0])));
+    public function verifyKey(array $keyHeader): bool {
+        return 1 === count($keyHeader) && 16 === strlen(base64_decode($keyHeader[0]));
     }
 
     /**
@@ -122,33 +120,33 @@ class RequestVerifier {
      * @param string[] $versionHeader MUST equal ["13"]
      * @return bool
      */
-    public function verifyVersion(array $versionHeader) {
-        return (1 === count($versionHeader) && static::VERSION === (int)$versionHeader[0]);
+    public function verifyVersion(array $versionHeader): bool {
+        return 1 === count($versionHeader) && static::VERSION === (int)$versionHeader[0];
     }
 
     /**
      * @todo Write logic for this method.  See section 4.2.1.8
      */
-    public function verifyProtocol($val) {
+    public function verifyProtocol($val): bool {
+        return true;
     }
 
     /**
      * @todo Write logic for this method.  See section 4.2.1.9
      */
-    public function verifyExtensions($val) {
+    public function verifyExtensions($val): bool {
+        return true;
     }
 
-    public function getPermessageDeflateOptions(array $requestHeader, array $responseHeader) {
+    public function getPermessageDeflateOptions(array $requestHeader, array $responseHeader): array {
+        $headerChecker = static fn (string $val) => 'permessage-deflate' === substr($val, 0, strlen('permessage-deflate'));
+
         $deflate = true;
-        if (!isset($requestHeader['Sec-WebSocket-Extensions']) || count(array_filter($requestHeader['Sec-WebSocket-Extensions'], function ($val) {
-            return 'permessage-deflate' === substr($val, 0, strlen('permessage-deflate'));
-        })) === 0) {
+        if (!isset($requestHeader['Sec-WebSocket-Extensions']) || count(array_filter($requestHeader['Sec-WebSocket-Extensions'], $headerChecker)) === 0) {
              $deflate = false;
         }
 
-        if (!isset($responseHeader['Sec-WebSocket-Extensions']) || count(array_filter($responseHeader['Sec-WebSocket-Extensions'], function ($val) {
-                return 'permessage-deflate' === substr($val, 0, strlen('permessage-deflate'));
-            })) === 0) {
+        if (!isset($responseHeader['Sec-WebSocket-Extensions']) || count(array_filter($responseHeader['Sec-WebSocket-Extensions'], $headerChecker)) === 0) {
             $deflate = false;
         }
 
diff --git a/src/Handshake/ResponseVerifier.php b/src/Handshake/ResponseVerifier.php
index 453f9d6..56c62c2 100644
--- a/src/Handshake/ResponseVerifier.php
+++ b/src/Handshake/ResponseVerifier.php
@@ -4,7 +4,7 @@ use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 
 class ResponseVerifier {
-    public function verifyAll(RequestInterface $request, ResponseInterface $response) {
+    public function verifyAll(RequestInterface $request, ResponseInterface $response): bool {
         $passes = 0;
 
         $passes += (int)$this->verifyStatus($response->getStatusCode());
@@ -26,31 +26,31 @@ class ResponseVerifier {
         return (6 === $passes);
     }
 
-    public function verifyStatus($status) {
-        return ((int)$status === 101);
+    public function verifyStatus(int $status): bool {
+        return $status === 101;
     }
 
-    public function verifyUpgrade(array $upgrade) {
-        return (in_array('websocket', array_map('strtolower', $upgrade)));
+    public function verifyUpgrade(array $upgrade): bool {
+        return in_array('websocket', array_map('strtolower', $upgrade));
     }
 
-    public function verifyConnection(array $connection) {
-        return (in_array('upgrade', array_map('strtolower', $connection)));
+    public function verifyConnection(array $connection): bool {
+        return in_array('upgrade', array_map('strtolower', $connection));
     }
 
-    public function verifySecWebSocketAccept($swa, $key) {
-        return (
+    public function verifySecWebSocketAccept(array $swa, array $key): bool {
+        return
             1 === count($swa) &&
             1 === count($key) &&
             $swa[0] === $this->sign($key[0])
-        );
+        ;
     }
 
-    public function sign($key) {
+    public function sign(string $key): string {
         return base64_encode(sha1($key . NegotiatorInterface::GUID, true));
     }
 
-    public function verifySubProtocol(array $requestHeader, array $responseHeader) {
+    public function verifySubProtocol(array $requestHeader, array $responseHeader): bool {
         if (0 === count($responseHeader)) {
             return true;
         }
@@ -60,7 +60,7 @@ class ResponseVerifier {
         return count($responseHeader) === 1 && count(array_intersect($responseHeader, $requestedProtocols)) === 1;
     }
 
-    public function verifyExtensions(array $requestHeader, array $responseHeader) {
+    public function verifyExtensions(array $requestHeader, array $responseHeader): int {
         if (in_array('permessage-deflate', $responseHeader)) {
             return strpos(implode(',', $requestHeader), 'permessage-deflate') !== false ? 1 : 0;
         }
diff --git a/src/Handshake/ServerNegotiator.php b/src/Handshake/ServerNegotiator.php
index e4ce79b..ab13e81 100644
--- a/src/Handshake/ServerNegotiator.php
+++ b/src/Handshake/ServerNegotiator.php
@@ -2,22 +2,20 @@
 namespace Ratchet\RFC6455\Handshake;
 use Psr\Http\Message\RequestInterface;
 use GuzzleHttp\Psr7\Response;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * The latest version of the WebSocket protocol
  * @todo Unicode: return mb_convert_encoding(pack("N",$u), mb_internal_encoding(), 'UCS-4BE');
  */
 class ServerNegotiator implements NegotiatorInterface {
-    /**
-     * @var \Ratchet\RFC6455\Handshake\RequestVerifier
-     */
-    private $verifier;
+    private RequestVerifier $verifier;
 
-    private $_supportedSubProtocols = [];
+    private array $_supportedSubProtocols = [];
 
-    private $_strictSubProtocols = false;
+    private bool $_strictSubProtocols = false;
 
-    private $enablePerMessageDeflate = false;
+    private bool $enablePerMessageDeflate = false;
 
     public function __construct(RequestVerifier $requestVerifier, $enablePerMessageDeflate = false) {
         $this->verifier = $requestVerifier;
@@ -38,21 +36,21 @@ class ServerNegotiator implements NegotiatorInterface {
     /**
      * {@inheritdoc}
      */
-    public function isProtocol(RequestInterface $request) {
+    public function isProtocol(RequestInterface $request): bool {
         return $this->verifier->verifyVersion($request->getHeader('Sec-WebSocket-Version'));
     }
 
     /**
      * {@inheritdoc}
      */
-    public function getVersionNumber() {
+    public function getVersionNumber(): int {
         return RequestVerifier::VERSION;
     }
 
     /**
      * {@inheritdoc}
      */
-    public function handshake(RequestInterface $request) {
+    public function handshake(RequestInterface $request): ResponseInterface {
         if (true !== $this->verifier->verifyMethod($request->getMethod())) {
             return new Response(405, ['Allow' => 'GET']);
         }
@@ -98,9 +96,7 @@ class ServerNegotiator implements NegotiatorInterface {
         if (count($subProtocols) > 0 || (count($this->_supportedSubProtocols) > 0 && $this->_strictSubProtocols)) {
             $subProtocols = array_map('trim', explode(',', implode(',', $subProtocols)));
 
-            $match = array_reduce($subProtocols, function($accumulator, $protocol) {
-                return $accumulator ?: (isset($this->_supportedSubProtocols[$protocol]) ? $protocol : null);
-            }, null);
+            $match = array_reduce($subProtocols, fn ($accumulator, $protocol) => $accumulator ?: (isset($this->_supportedSubProtocols[$protocol]) ? $protocol : null), null);
 
             if ($this->_strictSubProtocols && null === $match) {
                 return new Response(426, $upgradeSuggestion, null, '1.1', 'No Sec-WebSocket-Protocols requested supported');
@@ -137,14 +133,14 @@ class ServerNegotiator implements NegotiatorInterface {
      * @return string
      * @internal
      */
-    public function sign($key) {
+    public function sign(string $key): string {
         return base64_encode(sha1($key . static::GUID, true));
     }
 
     /**
      * @param array $protocols
      */
-    function setSupportedSubProtocols(array $protocols) {
+    public function setSupportedSubProtocols(array $protocols): void {
         $this->_supportedSubProtocols = array_flip($protocols);
     }
 
@@ -153,10 +149,10 @@ class ServerNegotiator implements NegotiatorInterface {
      *  will not upgrade if a match between request and supported subprotocols
      * @param boolean $enable
      * @todo Consider extending this interface and moving this there.
-     *       The spec does says the server can fail for this reason, but
-     * it is not a requirement. This is an implementation detail.
+     *       The spec does say the server can fail for this reason, but
+     *       it is not a requirement. This is an implementation detail.
      */
-    function setStrictSubProtocolCheck($enable) {
-        $this->_strictSubProtocols = (boolean)$enable;
+    public function setStrictSubProtocolCheck(bool $enable): void {
+        $this->_strictSubProtocols = $enable;
     }
 }
diff --git a/src/Messaging/CloseFrameChecker.php b/src/Messaging/CloseFrameChecker.php
index 3d800e5..78435c9 100644
--- a/src/Messaging/CloseFrameChecker.php
+++ b/src/Messaging/CloseFrameChecker.php
@@ -2,23 +2,19 @@
 namespace Ratchet\RFC6455\Messaging;
 
 class CloseFrameChecker {
-    private $validCloseCodes = [];
+    private array $validCloseCodes = [
+        Frame::CLOSE_NORMAL,
+        Frame::CLOSE_GOING_AWAY,
+        Frame::CLOSE_PROTOCOL,
+        Frame::CLOSE_BAD_DATA,
+        Frame::CLOSE_BAD_PAYLOAD,
+        Frame::CLOSE_POLICY,
+        Frame::CLOSE_TOO_BIG,
+        Frame::CLOSE_MAND_EXT,
+        Frame::CLOSE_SRV_ERR,
+    ];
 
-    public function __construct() {
-        $this->validCloseCodes = [
-            Frame::CLOSE_NORMAL,
-            Frame::CLOSE_GOING_AWAY,
-            Frame::CLOSE_PROTOCOL,
-            Frame::CLOSE_BAD_DATA,
-            Frame::CLOSE_BAD_PAYLOAD,
-            Frame::CLOSE_POLICY,
-            Frame::CLOSE_TOO_BIG,
-            Frame::CLOSE_MAND_EXT,
-            Frame::CLOSE_SRV_ERR,
-        ];
-    }
-
-    public function __invoke($val) {
+    public function __invoke(int $val): bool {
         return ($val >= 3000 && $val <= 4999) || in_array($val, $this->validCloseCodes);
     }
 }
diff --git a/src/Messaging/DataInterface.php b/src/Messaging/DataInterface.php
index 18aa2e3..1bdef36 100644
--- a/src/Messaging/DataInterface.php
+++ b/src/Messaging/DataInterface.php
@@ -1,34 +1,28 @@
 <?php
 namespace Ratchet\RFC6455\Messaging;
 
-interface DataInterface {
+interface DataInterface extends \Stringable {
     /**
      * Determine if the message is complete or still fragmented
      * @return bool
      */
-    function isCoalesced();
+    public function isCoalesced(): bool;
 
     /**
      * Get the number of bytes the payload is set to be
      * @return int
      */
-    function getPayloadLength();
+    public function getPayloadLength(): int;
 
     /**
      * Get the payload (message) sent from peer
      * @return string
      */
-    function getPayload();
+    public function getPayload(): string;
 
     /**
      * Get raw contents of the message
      * @return string
      */
-    function getContents();
-
-    /**
-     * Should return the unmasked payload received from peer
-     * @return string
-     */
-    function __toString();
+    public function getContents(): string;
 }
diff --git a/src/Messaging/Frame.php b/src/Messaging/Frame.php
index 63da6d2..8bc9265 100644
--- a/src/Messaging/Frame.php
+++ b/src/Messaging/Frame.php
@@ -26,40 +26,34 @@ class Frame implements FrameInterface {
 
     /**
      * The contents of the frame
-     * @var string
      */
-    protected $data = '';
+    protected string $data = '';
 
     /**
      * Number of bytes received from the frame
-     * @var int
      */
-    public $bytesRecvd = 0;
+    public int $bytesRecvd = 0;
 
     /**
      * Number of bytes in the payload (as per framing protocol)
-     * @var int
      */
-    protected $defPayLen = -1;
+    protected int $defPayLen = -1;
 
     /**
      * If the frame is coalesced this is true
      * This is to prevent doing math every time ::isCoalesced is called
-     * @var boolean
      */
-    private $isCoalesced = false;
+    private bool $isCoalesced = false;
 
     /**
      * The unpacked first byte of the frame
-     * @var int
      */
-    protected $firstByte = -1;
+    protected int $firstByte = -1;
 
     /**
      * The unpacked second byte of the frame
-     * @var int
      */
-    protected $secondByte = -1;
+    protected int $secondByte = -1;
 
     /**
      * @var callable
@@ -73,10 +67,8 @@ class Frame implements FrameInterface {
      * @param int         $opcode
      * @param callable<\UnderflowException> $ufExceptionFactory
      */
-    public function __construct($payload = null, $final = true, $opcode = 1, callable $ufExceptionFactory = null) {
-        $this->ufeg = $ufExceptionFactory ?: static function($msg = '') {
-            return new \UnderflowException($msg);
-        };
+    public function __construct(?string $payload = null, bool $final = true, int $opcode = 1, callable $ufExceptionFactory = null) {
+        $this->ufeg = $ufExceptionFactory ?: static fn (string $msg = '') => new \UnderflowException($msg);
 
         if (null === $payload) {
             return;
@@ -103,7 +95,7 @@ class Frame implements FrameInterface {
     /**
      * {@inheritdoc}
      */
-    public function isCoalesced() {
+    public function isCoalesced(): bool {
         if (true === $this->isCoalesced) {
             return true;
         }
@@ -123,7 +115,7 @@ class Frame implements FrameInterface {
     /**
      * {@inheritdoc}
      */
-    public function addBuffer($buf) {
+    public function addBuffer(string $buf): void {
         $len = strlen($buf);
 
         $this->data       .= $buf;
@@ -141,7 +133,7 @@ class Frame implements FrameInterface {
     /**
      * {@inheritdoc}
      */
-    public function isFinal() {
+    public function isFinal(): bool {
         if (-1 === $this->firstByte) {
             throw call_user_func($this->ufeg, 'Not enough bytes received to determine if this is the final frame in message');
         }
@@ -149,7 +141,7 @@ class Frame implements FrameInterface {
         return 128 === ($this->firstByte & 128);
     }
 
-    public function setRsv1($value = true) {
+    public function setRsv1(bool $value = true): self {
         if (strlen($this->data) == 0) {
             throw new \UnderflowException("Cannot set Rsv1 because there is no data.");
         }
@@ -170,7 +162,7 @@ class Frame implements FrameInterface {
      * @return boolean
      * @throws \UnderflowException
      */
-    public function getRsv1() {
+    public function getRsv1(): bool {
         if (-1 === $this->firstByte) {
             throw call_user_func($this->ufeg, 'Not enough bytes received to determine reserved bit');
         }
@@ -182,7 +174,7 @@ class Frame implements FrameInterface {
      * @return boolean
      * @throws \UnderflowException
      */
-    public function getRsv2() {
+    public function getRsv2(): bool {
         if (-1 === $this->firstByte) {
             throw call_user_func($this->ufeg, 'Not enough bytes received to determine reserved bit');
         }
@@ -194,7 +186,7 @@ class Frame implements FrameInterface {
      * @return boolean
      * @throws \UnderflowException
      */
-    public function getRsv3() {
+    public function getRsv3(): bool {
         if (-1 === $this->firstByte) {
             throw call_user_func($this->ufeg, 'Not enough bytes received to determine reserved bit');
         }
@@ -205,7 +197,7 @@ class Frame implements FrameInterface {
     /**
      * {@inheritdoc}
      */
-    public function isMasked() {
+    public function isMasked(): bool {
         if (-1 === $this->secondByte) {
             throw call_user_func($this->ufeg, "Not enough bytes received ({$this->bytesRecvd}) to determine if mask is set");
         }
@@ -216,7 +208,7 @@ class Frame implements FrameInterface {
     /**
      * {@inheritdoc}
      */
-    public function getMaskingKey() {
+    public function getMaskingKey(): string {
         if (!$this->isMasked()) {
             return '';
         }
@@ -234,7 +226,7 @@ class Frame implements FrameInterface {
      * Create a 4 byte masking key
      * @return string
      */
-    public function generateMaskingKey() {
+    public function generateMaskingKey(): string {
         $mask = '';
 
         for ($i = 1; $i <= static::MASK_LENGTH; $i++) {
@@ -251,7 +243,7 @@ class Frame implements FrameInterface {
      * @throws \InvalidArgumentException If there is an issue with the given masking key
      * @return Frame
      */
-    public function maskPayload($maskingKey = null) {
+    public function maskPayload(?string $maskingKey = null): self {
         if (null === $maskingKey) {
             $maskingKey = $this->generateMaskingKey();
         }
@@ -282,7 +274,7 @@ class Frame implements FrameInterface {
      * @throws \UnderFlowException If the frame is not coalesced
      * @return Frame
      */
-    public function unMaskPayload() {
+    public function unMaskPayload(): self {
         if (!$this->isCoalesced()) {
             throw call_user_func($this->ufeg, 'Frame must be coalesced before applying mask');
         }
@@ -311,7 +303,7 @@ class Frame implements FrameInterface {
      * @throws \UnderflowException If using the payload but enough hasn't been buffered
      * @return string              The masked string
      */
-    public function applyMask($maskingKey, $payload = null) {
+    public function applyMask(string $maskingKey, ?string $payload = null): string {
         if (null === $payload) {
             if (!$this->isCoalesced()) {
                 throw call_user_func($this->ufeg, 'Frame must be coalesced to apply a mask');
@@ -332,7 +324,7 @@ class Frame implements FrameInterface {
     /**
      * {@inheritdoc}
      */
-    public function getOpcode() {
+    public function getOpcode(): int {
         if (-1 === $this->firstByte) {
             throw call_user_func($this->ufeg, 'Not enough bytes received to determine opcode');
         }
@@ -345,7 +337,7 @@ class Frame implements FrameInterface {
      * @return int
      * @throws \UnderflowException If the buffer doesn't have enough data to determine this
      */
-    protected function getFirstPayloadVal() {
+    protected function getFirstPayloadVal(): int {
         if (-1 === $this->secondByte) {
             throw call_user_func($this->ufeg, 'Not enough bytes received');
         }
@@ -357,7 +349,7 @@ class Frame implements FrameInterface {
      * @return int (7|23|71) Number of bits defined for the payload length in the fame
      * @throws \UnderflowException
      */
-    protected function getNumPayloadBits() {
+    protected function getNumPayloadBits(): int {
         if (-1 === $this->secondByte) {
             throw call_user_func($this->ufeg, 'Not enough bytes received');
         }
@@ -387,14 +379,14 @@ class Frame implements FrameInterface {
      * This just returns the number of bytes used in the frame to describe the payload length (as opposed to # of bits)
      * @see getNumPayloadBits
      */
-    protected function getNumPayloadBytes() {
+    protected function getNumPayloadBytes(): int {
         return (1 + $this->getNumPayloadBits()) / 8;
     }
 
     /**
      * {@inheritdoc}
      */
-    public function getPayloadLength() {
+    public function getPayloadLength(): int {
         if ($this->defPayLen !== -1) {
             return $this->defPayLen;
         }
@@ -424,7 +416,7 @@ class Frame implements FrameInterface {
     /**
      * {@inheritdoc}
      */
-    public function getPayloadStartingByte() {
+    public function getPayloadStartingByte(): int {
         return 1 + $this->getNumPayloadBytes() + ($this->isMasked() ? static::MASK_LENGTH : 0);
     }
 
@@ -432,7 +424,7 @@ class Frame implements FrameInterface {
      * {@inheritdoc}
      * @todo Consider not checking mask, always returning the payload, masked or not
      */
-    public function getPayload() {
+    public function getPayload(): string {
         if (!$this->isCoalesced()) {
             throw call_user_func($this->ufeg, 'Can not return partial message');
         }
@@ -444,11 +436,11 @@ class Frame implements FrameInterface {
      * Get the raw contents of the frame
      * @todo This is untested, make sure the substr is right - trying to return the frame w/o the overflow
      */
-    public function getContents() {
+    public function getContents(): string {
         return substr($this->data, 0, $this->getPayloadStartingByte() + $this->getPayloadLength());
     }
 
-    public function __toString() {
+    public function __toString(): string {
         $payload = (string)substr($this->data, $this->getPayloadStartingByte(), $this->getPayloadLength());
 
         if ($this->isMasked()) {
@@ -463,7 +455,7 @@ class Frame implements FrameInterface {
      * This method will take the extra bytes off the end and return them
      * @return string
      */
-    public function extractOverflow() {
+    public function extractOverflow(): string {
         if ($this->isCoalesced()) {
             $endPoint  = $this->getPayloadLength();
             $endPoint += $this->getPayloadStartingByte();
diff --git a/src/Messaging/FrameInterface.php b/src/Messaging/FrameInterface.php
index dc24091..4d8fe68 100644
--- a/src/Messaging/FrameInterface.php
+++ b/src/Messaging/FrameInterface.php
@@ -6,33 +6,33 @@ interface FrameInterface extends DataInterface {
      * Add incoming data to the frame from peer
      * @param string
      */
-    function addBuffer($buf);
+    public function addBuffer(string $buf): void;
 
     /**
      * Is this the final frame in a fragmented message?
      * @return bool
      */
-    function isFinal();
+    public function isFinal(): bool;
 
     /**
      * Is the payload masked?
      * @return bool
      */
-    function isMasked();
+    public function isMasked(): bool;
 
     /**
      * @return int
      */
-    function getOpcode();
+    public function getOpcode(): int;
 
     /**
      * @return int
      */
-    //function getReceivedPayloadLength();
+    //public function getReceivedPayloadLength(): int;
 
     /**
      * 32-big string
      * @return string
      */
-    function getMaskingKey();
+    public function getMaskingKey(): string;
 }
diff --git a/src/Messaging/Message.php b/src/Messaging/Message.php
index aea2050..287b1fa 100644
--- a/src/Messaging/Message.php
+++ b/src/Messaging/Message.php
@@ -2,53 +2,43 @@
 namespace Ratchet\RFC6455\Messaging;
 
 class Message implements \IteratorAggregate, MessageInterface {
-    /**
-     * @var \SplDoublyLinkedList
-     */
-    private $_frames;
+    private \SplDoublyLinkedList $_frames;
 
-    /**
-     * @var int
-     */
-    private $len;
+    private int $len;
 
-    #[\ReturnTypeWillChange]
     public function __construct() {
         $this->_frames = new \SplDoublyLinkedList;
         $this->len = 0;
     }
 
-    #[\ReturnTypeWillChange]
-    public function getIterator() {
+    public function getIterator(): \Traversable {
         return $this->_frames;
     }
 
     /**
      * {@inheritdoc}
      */
-    #[\ReturnTypeWillChange]
-    public function count() {
+    public function count(): int {
         return count($this->_frames);
     }
 
     /**
      * {@inheritdoc}
      */
-    #[\ReturnTypeWillChange]
-    public function isCoalesced() {
+    public function isCoalesced(): bool {
         if (count($this->_frames) == 0) {
             return false;
         }
 
         $last = $this->_frames->top();
 
-        return ($last->isCoalesced() && $last->isFinal());
+        return $last->isCoalesced() && $last->isFinal();
     }
 
     /**
      * {@inheritdoc}
      */
-    public function addFrame(FrameInterface $fragment) {
+    public function addFrame(FrameInterface $fragment): MessageInterface {
         $this->len += $fragment->getPayloadLength();
         $this->_frames->push($fragment);
 
@@ -58,7 +48,7 @@ class Message implements \IteratorAggregate, MessageInterface {
     /**
      * {@inheritdoc}
      */
-    public function getOpcode() {
+    public function getOpcode(): int {
         if (count($this->_frames) == 0) {
             throw new \UnderflowException('No frames have been added to this message');
         }
@@ -69,14 +59,14 @@ class Message implements \IteratorAggregate, MessageInterface {
     /**
      * {@inheritdoc}
      */
-    public function getPayloadLength() {
+    public function getPayloadLength(): int {
         return $this->len;
     }
 
     /**
      * {@inheritdoc}
      */
-    public function getPayload() {
+    public function getPayload(): string {
         if (!$this->isCoalesced()) {
             throw new \UnderflowException('Message has not been put back together yet');
         }
@@ -87,7 +77,7 @@ class Message implements \IteratorAggregate, MessageInterface {
     /**
      * {@inheritdoc}
      */
-    public function getContents() {
+    public function getContents(): string {
         if (!$this->isCoalesced()) {
             throw new \UnderflowException("Message has not been put back together yet");
         }
@@ -101,7 +91,7 @@ class Message implements \IteratorAggregate, MessageInterface {
         return $buffer;
     }
 
-    public function __toString() {
+    public function __toString(): string {
         $buffer = '';
 
         foreach ($this->_frames as $frame) {
@@ -114,7 +104,7 @@ class Message implements \IteratorAggregate, MessageInterface {
     /**
      * @return boolean
      */
-    public function isBinary() {
+    public function isBinary(): bool {
         if ($this->_frames->isEmpty()) {
             throw new \UnderflowException('Not enough data has been received to determine if message is binary');
         }
@@ -125,7 +115,7 @@ class Message implements \IteratorAggregate, MessageInterface {
     /**
      * @return boolean
      */
-    public function getRsv1() {
+    public function getRsv1(): bool {
         if ($this->_frames->isEmpty()) {
             return false;
             //throw new \UnderflowException('Not enough data has been received to determine if message is binary');
diff --git a/src/Messaging/MessageBuffer.php b/src/Messaging/MessageBuffer.php
index 317a26a..1007c6a 100644
--- a/src/Messaging/MessageBuffer.php
+++ b/src/Messaging/MessageBuffer.php
@@ -4,25 +4,16 @@ namespace Ratchet\RFC6455\Messaging;
 use Ratchet\RFC6455\Handshake\PermessageDeflateOptions;
 
 class MessageBuffer {
-    /**
-     * @var \Ratchet\RFC6455\Messaging\CloseFrameChecker
-     */
-    private $closeFrameChecker;
+    private CloseFrameChecker $closeFrameChecker;
 
     /**
      * @var callable
      */
     private $exceptionFactory;
 
-    /**
-     * @var \Ratchet\RFC6455\Messaging\Message
-     */
-    private $messageBuffer;
+    private ?MessageInterface $messageBuffer = null;
 
-    /**
-     * @var \Ratchet\RFC6455\Messaging\Frame
-     */
-    private $frameBuffer;
+    private ?FrameInterface $frameBuffer = null;
 
     /**
      * @var callable
@@ -34,71 +25,55 @@ class MessageBuffer {
      */
     private $onControl;
 
-    /**
-     * @var bool
-     */
-    private $checkForMask;
+    private bool $checkForMask;
 
     /**
      * @var callable
      */
     private $sender;
 
-    /**
-     * @var string
-     */
-    private $leftovers;
+    private string $leftovers = '';
+
+    private int $streamingMessageOpCode = -1;
+
+    private PermessageDeflateOptions $permessageDeflateOptions;
+
+    private bool $deflateEnabled;
+
+    private int $maxMessagePayloadSize;
+
+    private int $maxFramePayloadSize;
+
+    private bool $compressedMessage = false;
 
     /**
-     * @var int
+     * @var resource|bool|null
      */
-    private $streamingMessageOpCode = -1;
+    private $inflator = null;
 
     /**
-     * @var PermessageDeflateOptions
+     * @var resource|bool|null
      */
-    private $permessageDeflateOptions;
+    private $deflator = null;
 
-    /**
-     * @var bool
-     */
-    private $deflateEnabled = false;
-
-    /**
-     * @var int
-     */
-    private $maxMessagePayloadSize;
-
-    /**
-     * @var int
-     */
-    private $maxFramePayloadSize;
-
-    /**
-     * @var bool
-     */
-    private $compressedMessage;
-
-    function __construct(
+    public function __construct(
         CloseFrameChecker $frameChecker,
         callable $onMessage,
-        callable $onControl = null,
-        $expectMask = true,
-        $exceptionFactory = null,
-        $maxMessagePayloadSize = null, // null for default - zero for no limit
-        $maxFramePayloadSize = null,   // null for default - zero for no limit
-        callable $sender = null,
-        PermessageDeflateOptions $permessageDeflateOptions = null
+        ?callable $onControl = null,
+        bool $expectMask = true,
+        ?callable $exceptionFactory = null,
+        ?int $maxMessagePayloadSize = null, // null for default - zero for no limit
+        ?int $maxFramePayloadSize = null,   // null for default - zero for no limit
+        ?callable $sender = null,
+        ?PermessageDeflateOptions $permessageDeflateOptions = null
     ) {
         $this->closeFrameChecker = $frameChecker;
-        $this->checkForMask = (bool)$expectMask;
+        $this->checkForMask = $expectMask;
 
-        $this->exceptionFactory ?: $exceptionFactory = function($msg) {
-            return new \UnderflowException($msg);
-        };
+        $this->exceptionFactory = $exceptionFactory ?: static fn (string $msg) => new \UnderflowException($msg);
 
         $this->onMessage = $onMessage;
-        $this->onControl = $onControl ?: function() {};
+        $this->onControl = $onControl ?: static function (): void {};
 
         $this->sender = $sender;
 
@@ -110,10 +85,6 @@ class MessageBuffer {
             throw new \InvalidArgumentException('sender must be set when deflate is enabled');
         }
 
-        $this->compressedMessage = false;
-
-        $this->leftovers = '';
-
         $memory_limit_bytes = static::getMemoryLimit();
 
         if ($maxMessagePayloadSize === null) {
@@ -123,18 +94,18 @@ class MessageBuffer {
             $maxFramePayloadSize = (int)($memory_limit_bytes / 4);
         }
 
-        if (!is_int($maxFramePayloadSize) || $maxFramePayloadSize > 0x7FFFFFFFFFFFFFFF || $maxFramePayloadSize < 0) { // this should be interesting on non-64 bit systems
+        if ($maxFramePayloadSize > 0x7FFFFFFFFFFFFFFF || $maxFramePayloadSize < 0) { // this should be interesting on non-64 bit systems
             throw new \InvalidArgumentException($maxFramePayloadSize . ' is not a valid maxFramePayloadSize');
         }
         $this->maxFramePayloadSize = $maxFramePayloadSize;
 
-        if (!is_int($maxMessagePayloadSize) || $maxMessagePayloadSize > 0x7FFFFFFFFFFFFFFF || $maxMessagePayloadSize < 0) {
+        if ($maxMessagePayloadSize > 0x7FFFFFFFFFFFFFFF || $maxMessagePayloadSize < 0) {
             throw new \InvalidArgumentException($maxMessagePayloadSize . 'is not a valid maxMessagePayloadSize');
         }
         $this->maxMessagePayloadSize = $maxMessagePayloadSize;
     }
 
-    public function onData($data) {
+    public function onData(string $data): void {
         $data = $this->leftovers . $data;
         $dataLen = strlen($data);
 
@@ -214,9 +185,9 @@ class MessageBuffer {
 
     /**
      * @param string $data
-     * @return null
+     * @return void
      */
-    private function processData($data) {
+    private function processData(string $data): void {
         $this->messageBuffer ?: $this->messageBuffer = $this->newMessage();
         $this->frameBuffer   ?: $this->frameBuffer   = $this->newFrame();
 
@@ -235,7 +206,7 @@ class MessageBuffer {
             $onControl($this->frameBuffer, $this);
 
             if (Frame::OP_CLOSE === $opcode) {
-                return '';
+                return;
             }
         } else {
             if ($this->messageBuffer->count() === 0 && $this->frameBuffer->getRsv1()) {
@@ -273,10 +244,10 @@ class MessageBuffer {
 
     /**
      * Check a frame to be added to the current message buffer
-     * @param \Ratchet\RFC6455\Messaging\FrameInterface|FrameInterface $frame
-     * @return \Ratchet\RFC6455\Messaging\FrameInterface|FrameInterface
+     * @param FrameInterface $frame
+     * @return FrameInterface
      */
-    public function frameCheck(FrameInterface $frame) {
+    public function frameCheck(FrameInterface $frame): FrameInterface {
         if ((false !== $frame->getRsv1() && !$this->deflateEnabled) ||
             false !== $frame->getRsv2() ||
             false !== $frame->getRsv3()
@@ -323,13 +294,11 @@ class MessageBuffer {
                     }
 
                     return $frame;
-                    break;
                 case Frame::OP_PING:
                 case Frame::OP_PONG:
                     break;
                 default:
                     return $this->newCloseFrame(Frame::CLOSE_PROTOCOL, 'Ratchet detected an invalid OP code');
-                    break;
             }
 
             return $frame;
@@ -348,7 +317,7 @@ class MessageBuffer {
 
     /**
      * Determine if a message is valid
-     * @param \Ratchet\RFC6455\Messaging\MessageInterface
+     * @param MessageInterface
      * @return bool|int true if valid - false if incomplete - int of recommended close code
      */
     public function checkMessage(MessageInterface $message) {
@@ -361,7 +330,7 @@ class MessageBuffer {
         return true;
     }
 
-    private function checkUtf8($string) {
+    private function checkUtf8(string $string): bool {
         if (extension_loaded('mbstring')) {
             return mb_check_encoding($string, 'UTF-8');
         }
@@ -370,27 +339,27 @@ class MessageBuffer {
     }
 
     /**
-     * @return \Ratchet\RFC6455\Messaging\MessageInterface
+     * @return MessageInterface
      */
-    public function newMessage() {
+    public function newMessage(): MessageInterface {
         return new Message;
     }
 
     /**
      * @param string|null $payload
-     * @param bool|null   $final
-     * @param int|null    $opcode
-     * @return \Ratchet\RFC6455\Messaging\FrameInterface
+     * @param bool        $final
+     * @param int         $opcode
+     * @return FrameInterface
      */
-    public function newFrame($payload = null, $final = null, $opcode = null) {
+    public function newFrame(?string $payload = null, bool $final = true, int $opcode = Frame::OP_TEXT): FrameInterface {
         return new Frame($payload, $final, $opcode, $this->exceptionFactory);
     }
 
-    public function newCloseFrame($code, $reason = '') {
+    public function newCloseFrame(int $code, string $reason = ''): FrameInterface {
         return $this->newFrame(pack('n', $code) . $reason, true, Frame::OP_CLOSE);
     }
 
-    public function sendFrame(Frame $frame) {
+    public function sendFrame(FrameInterface $frame): void {
         if ($this->sender === null) {
             throw new \Exception('To send frames using the MessageBuffer, sender must be set.');
         }
@@ -408,7 +377,7 @@ class MessageBuffer {
         $sender($frame->getContents());
     }
 
-    public function sendMessage($messagePayload, $final = true, $isBinary = false) {
+    public function sendMessage(string $messagePayload, bool $final = true, bool $isBinary = false): void {
         $opCode = $isBinary ? Frame::OP_BINARY : Frame::OP_TEXT;
         if ($this->streamingMessageOpCode === -1) {
             $this->streamingMessageOpCode = $opCode;
@@ -431,29 +400,27 @@ class MessageBuffer {
         }
     }
 
-    private $inflator;
-
-    private function getDeflateNoContextTakeover() {
+    private function getDeflateNoContextTakeover(): ?bool {
         return $this->checkForMask ?
             $this->permessageDeflateOptions->getServerNoContextTakeover() :
             $this->permessageDeflateOptions->getClientNoContextTakeover();
     }
 
-    private function getDeflateWindowBits() {
+    private function getDeflateWindowBits(): int {
         return $this->checkForMask ? $this->permessageDeflateOptions->getServerMaxWindowBits() : $this->permessageDeflateOptions->getClientMaxWindowBits();
     }
 
-    private function getInflateNoContextTakeover() {
+    private function getInflateNoContextTakeover(): ?bool {
         return $this->checkForMask ?
             $this->permessageDeflateOptions->getClientNoContextTakeover() :
             $this->permessageDeflateOptions->getServerNoContextTakeover();
     }
 
-    private function getInflateWindowBits() {
+    private function getInflateWindowBits(): int {
         return $this->checkForMask ? $this->permessageDeflateOptions->getClientMaxWindowBits() : $this->permessageDeflateOptions->getServerMaxWindowBits();
     }
 
-    private function inflateFrame(Frame $frame) {
+    private function inflateFrame(FrameInterface $frame): Frame {
         if ($this->inflator === null) {
             $this->inflator = inflate_init(
                 ZLIB_ENCODING_RAW,
@@ -480,16 +447,14 @@ class MessageBuffer {
         );
     }
 
-    private $deflator;
-
-    private function deflateFrame(Frame $frame)
+    private function deflateFrame(FrameInterface $frame): FrameInterface
     {
         if ($frame->getRsv1()) {
             return $frame; // frame is already deflated
         }
 
         if ($this->deflator === null) {
-            $bits = (int)$this->getDeflateWindowBits();
+            $bits = $this->getDeflateWindowBits();
             if ($bits === 8) {
                 $bits = 9;
             }
@@ -549,7 +514,7 @@ class MessageBuffer {
      * @param null|string $memory_limit
      * @return int
      */
-    private static function getMemoryLimit($memory_limit = null) {
+    private static function getMemoryLimit(?string $memory_limit = null): int {
         $memory_limit = $memory_limit === null ? \trim(\ini_get('memory_limit')) : $memory_limit;
         $memory_limit_bytes = 0;
         if ($memory_limit !== '') {
diff --git a/src/Messaging/MessageInterface.php b/src/Messaging/MessageInterface.php
index fd7212e..5244b81 100644
--- a/src/Messaging/MessageInterface.php
+++ b/src/Messaging/MessageInterface.php
@@ -6,15 +6,15 @@ interface MessageInterface extends DataInterface, \Traversable, \Countable {
      * @param FrameInterface $fragment
      * @return MessageInterface
      */
-    function addFrame(FrameInterface $fragment);
+    public function addFrame(FrameInterface $fragment): self;
 
     /**
      * @return int
      */
-    function getOpcode();
+    public function getOpcode(): int;
 
     /**
      * @return bool
      */
-    function isBinary();
+    public function isBinary(): bool;
 }
diff --git a/tests/unit/Messaging/MessageBufferTest.php b/tests/unit/Messaging/MessageBufferTest.php
index 47d203a..b3a9eef 100644
--- a/tests/unit/Messaging/MessageBufferTest.php
+++ b/tests/unit/Messaging/MessageBufferTest.php
@@ -294,7 +294,7 @@ class MessageBufferTest extends TestCase
             false,
             null,
             0,
-            0x8000000000000000
+            -1
         );
     }
 
@@ -307,7 +307,7 @@ class MessageBufferTest extends TestCase
             static function (Frame $frame): void {},
             false,
             null,
-            0x8000000000000000,
+            -1,
             0
         );
     }